Recently, with regard to connecting structure between a liquid-crystal panel and an external device, printed-circuit substrates, such as TAB (Tape Automated Bonding), FPC (Flexible Printed Circuit) and TCP, have been generally employed. IC chips for driving the liquid-crystal panel are assembled on the printed-circuit substrates, thereby achieving compactness and high functionality. Thus, the packaging density of IC chips is improved in a liquid crystal display wherein these substrates are employed.
Today, in liquid crystal displays having the above-mentioned liquid-crystal panels, thin-width TCPs, which have a smaller gap between the input terminal and the output terminal, have been widely used in order to further achieve compactness.
For example, as shown in FIGS. 4 and 5, a thin-width TCP, which is formed into a belt shape, is provided with an IC chip 31 that is used for driving the liquid-crystal panel. In the thin-width TCP 30, a plurality of output electrodes 32 and input electrodes 33, which are respectively connected to the terminals of the IC chip 31, are mounted on both sides of the IC chip 31 along the length of the thin-width TCP 30.
The output electrodes 32 are formed into a comb shape in an extending manner to the left from the IC chip 31 as shown in the drawings. The input electrodes 33 are also formed into a comb shape in an extending manner to the right from the IC chip 31 as shown in the drawings. Those output electrodes 32 and the input electrodes 33 are covered with a film portion 34 and supported thereby.
In the central portion of the thin-width TCP 30 is provided an opening 34b through which the IC chip 31 is connected to the output electrodes 32 and the input electrodes 33. Ends of the output electrodes 32 and the input electrodes 33 respectively stick out inside the opening 34b.
The opening 34b is filled with protective resin through a molding process; this allows the IC chip 31 to be connected to the output electrodes 32 and the input electrodes 33, and securely fixed therein. Thus, a resin mold section 36 is formed around the IC chip 31.
Further, in the film portion 34 is formed a slit 34a by removing a part of the film portion 34 at the vicinity of the end portion on the input side. Exposed terminals 33a of the input electrodes 33 are located inside the slit 34a so as to be soldered to electrodes of a printed-circuit substrate or other substrates.
The following description will discuss a connecting method where the thin-width TCP 30 is employed. In the case where the thin-width TCP 30 is used for connecting the liquid crystal panel and the printed-circuit substrate, the output electrodes 32 and electrodes, not shown, of a liquid crystal panel 40 are first connected respectively as shown in FIG. 6 by the use of an anisotropic conductive film or other materials.
The input electrodes 33, on the other hand, are connected to the respective electrodes 42 through solder 43. Thus, the printed-circuit substrate 41 and the liquid crystal panel 40 are electrically connected to each other through the thin-width TCP 30.
The connection between the thin-width TCP 30 and the printed-circuit substrate 41 through the solder 43 is made by using a soldering iron 44. In this case, however, the resin mold section 36, which is formed through the molding process of the IC chip 31, protrudes from the back side of the thin-width TCP 30; this protruding resin mold section 36 results in a step W.sub.O even when the terminals are pressed down by the soldering iron 44.
This causes the terminals 33a to be lifted from the printed-circuit substrate 41, and since the terminals 33a do not contact the electrodes 42 well, it is difficult to solder both of them.
Therefore, in a conventional method, the terminals 33a and the electrodes 42 are soldered while avoiding the influence of the step W.sub.O caused by the protruding resin mold section 36, as shown in FIG. 6.
More specifically, the printed-circuit substrate 41 is fixed in a slanted state by using a device for supporting the printed-circuit substrate 41, not shown. This arrangement makes it possible to bring the terminals 33a in contact with the electrodes 42 while avoiding the influence of the step W.sub.O caused by the protruding resin mold section 36.
Next, after fixing the resin mold section 36 and the printed-circuit substrate 41 by the use of a temporary securing tape 45, the terminals 33a and the electrodes 42 are soldered by pressing them to contact one another using the tip of the soldering iron 44.
However, this method, which uses the thin-width TCP 30 having the conventional structure and wherein soldering is made by the soldering iron 44 while holding the conventional printed-circuit substrate 41 in the slanted state, raises the following problems.
(1) Problems Associated with the Structure of the Conventional Thin-width TCP 30:
(a) The film portion 34 in the thin-width TCP 30 has elasticity to a certain degree. Therefore, in the conventional structure wherein the terminals 33a are situated in the slit 34a, the elasticity of the film portions 34 lying on both sides of the slit 34a in the thin-width TCP 30 in the length-wise direction gives adverse effects on the pliability of the terminals 33a.
Therefore, even if the terminals 33a are pressed so as to bring them into contact with the electrodes 42, the terminals 33a tend to be lifted up, resulting in difficulty in contacting both of them.
The contact between them becomes even worse when the printed-circuit substrate 41 or the liquid crystal panel 40 has warping or when the thin-width TCP 30 has a curl-distortion in its own structure. This results in reliability problem in the connected structure between them.
(b) In particular, in the printed-circuit substrates such as thin-width TCPs 30 wherein the IC chip 31 and the slit 34a are closely located, when the thin-width TCP 30 is bent by pressing its terminals 33a using the tip of the soldering iron 44, the distortion stress may affect the resin mold section 36 and cause cracking in the resin mold section 36, if the portion of the slit 34a does not have sufficient pliability.
(2) Problems Associated With the Connecting Method:
(a) In the conventional connecting method, since the tip of the soldering iron 44 has to be brought into contact with the slanting portion, it is difficult to keep the tip stably contacting with the connecting portion. For this reason, it is hard to obtain stable solder quality and to improve the reliability of the connecting structure.
(b) The soldering iron 44 is susceptible to wear in its tip; this also makes it difficult to obtain stable solder quality and to improve the reliability of the connecting structure.
(c) The tip of the soldering iron 44 might be caught by the exposed terminals 33a, causing cutoffs in them especially when the exposed terminals 33a have narrow terminal pitches and are made of thin copper foil.
(d) As is described in (b) of (1), in the printed-circuit substrates such as thin-width TCP 30s wherein the IC chip 31 and the slit 34a are closely located, when the thin-width TCP 30 is bent by pressing its terminals 33a using the tip of the soldering iron 44, the distortion stress may affect the resin mold section 36 and cause cracking in the resin mold section 36.